1. Field of the Invention
Various implementations of the present invention are directed to an amplified bimorph scanning mirror for use in various optical systems and method of manufacturing thereof. Exemplary implementations of the present invention are also directed to an optical coherence tomography scanner incorporating the amplified bimorph scanning mirror. Exemplary implementations of the invention are further directed to a method of optically scanning a target site using the amplified bimorph scanning mirror. A scan range which can be obtained by exemplary implementations of the present invention can be larger than the scan range made available by conventional scanners.
2. Description of the Related Art
Optical coherence tomography (OCT) is an optical imaging technique analogous to ultrasound that uses partially coherent pulses of infrared light to interrogate the target and create images of sub-surface microscopic structures with a resolution of 10 μm or less.See Fercher, A. F., “Optical Coherence Tomography,” Journal of Biomedical Optics, Vol. 1, No. 3, 157-173 (1996). The time delay of the received echoes is detected with interferometry, so a map of reflectivity versus optical depth can be created. OCT has been shown to produce images with high spatial resolution and penetration depths ranging from 1 to 3 mm.See Fujimoto, J. G., et al., “Optical biopsy and imaging using optical coherence tomography,” Nature Medicine , Vol. 1, No. 9, 970-972 (1995). One of the first clinical application of OCT was in ophthalmology due to the ideal optical imaging environment in the eye.See Id. OCT has also shown great promise in other applications including intravascular imaging, imaging of the bladder and urinary tract and imaging of the lining of the gastrointestinal tract. See Id.
OCT creates a single line of data through a target. Therefore it is necessary to steer the infrared beam across the target and compile the individual data lines to form two- or three-dimensional images. This makes the beam scanning methodology and apparatus implementing the methodology one of the more critical aspects of an OCT system. Conventional scanning methods are mechanical and use galvanometers and other actuation techniques to steer the infrared beam across the target. A desirable feature for a scanning technique is to use a mirror structure facilitating minimally invasive medical interventions. Accordingly, a compact scanning method and a device for implementing such a method are needed.
Various conventional methods have been investigated for scanning the OCT beam for use in minimally invasive applications. For example, one conventional endoscopic OCT (EOCT) system design used in clinical trials uses a spinning reflective element to scan the infrared beam across the tissue in a circular side-scanning configuration.See Tearney, G., et al., “In Vivo Endoscopic Optical Biopsy with Optical Coherence Tomography,” Science , Vol. 236, 2037-2039 (1997). See also Rollins, A. M., et al. “Real-time in vivo imaging of human gastrointestinal ultrastructure by use of endoscopic optical coherence tomography with a novel efficient interferometer design,” Optics Letters , Vol. 24, 1358-1360 (1999). However, this conventional scanning arrangement allows the imaging probe to view targets only directly adjacent to the probe. On the other hand, a sectorscanning probe can enable the creation of images in a large sector to the side or front of the probe to guide interventional procedures conducted using instruments that are introduced concurrently with the imaging device.
Several conventional OCT probes have been developed which image in a non-circumferential scan geometry. These include probes that use piezoelectric bimorphs to scan the imaging fiber,see Boppart, S. A., et al., “Forward-imaging instruments for optical coherence tomography,” Optics Letters, Vol. 22, 1618-1620 (1997), probes that use thermoelectric actuators to swing a scanning mirror, see Pan, Y., et al., “Endoscopic optical coherence tomography based on a microelectromechanical mirror,” Optics Letters, Vol. 26, 1966-1968 (2001), probes that use a linear-scanning galvanometer to move the optics in a catheter probe, see Bouma, B. E. and G. J. Tearney, “Power-efficient nonreciprocal interferometer and linear-scanning fiber-optic catheter for optical coherence tomography,” Optics Letters, Vol. 24, 531-533 (1999), and probes that use optical beam steering using different MEMS actuators, see Zara, J. M. and S. W. Smith, “Optical Scanner Using a MEMS Actuator,” Sensors and Actuators: A: Physical, 102 (1-2): 176-184 (2002).
However, still larger scan ranges than those provided by the above-mentioned sector-scanning probes are desired.